OP
Tell them to read expatsingapore forum. Your classmates will
soon learn their English is pretty sh*t compared to Westerners, and
that Westerners think Singaporean English is c.r.a.p.
The difference between you and local Singaporeans is that you
are honest. You know your English is not perfect and are trying to
improve it. Singaporeans, on the other hand, actually think they
can speak it. I've seen a Singaporean actually try to correct
Asians from overseas by teaching them Singlish, when the Asian was
actually speaking fluent English!
Just last week I was at McDonalds and asked for a large Coke
Light for my meal. The Singaporean guy was teaching a girl from
China. The girl from China keyed in my order, and the Singaporean
told her off telling her she was wrong.
Lo and behold, the Singaporean guy gives me a small normal Coke,
and large French Fries instead of normal fries and large Coke
Light. I then tell the girl in mandarin that she was right.
Singaporean's English is not very good and her English was correct,
and not to doubt herself.
So OP- be brave and perservere! Tell your oh so smart
classmates to go and talk to a group of Westerners and see if the
Westerners think their English is good.